Method of manufacturing sintered permanent magnets



United States Patent METHOD OF MANUFACTURING SINTERED PERMANENT MAGNETS Gerard Hugo Weber and Petrus Johannes Hakker, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Application September 8, 1954 Serial No. 454,853

Claims priority, application Netherlands September 9, 1953 3 Claims. (Cl. 29155.6)

This invention relates to a method of manufacturing sintered permanent magnets. More particularly, this invention relates to the premagnetization of bodies of magnetic materials prior to the sintering process.

Magnetic bodies which are formed from powdered magnetic materials without the use of mechanical binding agents at temperatures below their Curie point, usually at room} temperatures, and magnetized and pressed before sintering are generally very fragile. Consequently, such molded bodies are apt to become damaged or deteriorate prior to the subsequent sintering process. These bodies may be damaged as a result of collisions due to mutual attraction of the bodies during transportation to the sintering ovens or they may disintegrate of their own accord if the coherence of the material is exceeded by the internal magnetic repulsion of adjacent particles.

The principal object of this invention is to reduce the damage and deterioration of molded magnetic bodies before sintering.

In accordance with this invention a method of manufacturing sintered permanent magnets is provided in which finely-divided particles of permanent magnetic material in either a dry or suspended state are formed into bodies by a molding operation and anisotropically magnetized by a magnetic field during the molding operation and thereafter at least partially demagnetized and sintered.

The magnetic material utilized in this invention consists of a body built up mainly of hexagonal crystals having dimensions not exceeding 10,11, and having the composition of MO.6Fe O or MFe O in which M represents one of the metals selected from group consisting of Ba, Sr and Pb, with the possible partial replacement of not more than an atomic fraction of 0.4 of one or more of these metals by calcium. These materials are fully gdescribed and claimed in British Patent No. 708,127,

April 28, 1954, and the method of making sintered anisotropic magnets from finely divided materials of said composition are fully set forth and claimed in copending US. application Ser. No. 325,202, filed December 10, 1952, now US. Patent 2,762,778.

The molded magnetic materials described above are preferably demagnetized by subjecting them to a demagnetizing field having a strength at least approximately equal to the field strength of disappearance or the intrinsic coercive force, H of the material. Although it was expected that the demagnetization of the molded product would appreciably disorient the directed crystallites, it was surprising to find from the following examples of a sintered permanent magnet consisting of the above materials that hardly any disorientation appears even though the magnet had become partially demagnetized before sintering.

in order that the invention may be clearly understood and readily carried into efiect we shall describe the same in connection with the following example, having the ice composition BaO.6Fe O the powder was in a suspended state.

Thus it is apparent that the method of our invention is useful in reducing the collisions of these magnetic bodies before sintering and thus preventing injury to these bodies.

What is claimed is:

1. A method of manufacturing sintered permanent magnets comprising the steps, compacting finely-divided permanent magnet forming material, while in the presence of a magnetic field, into a plurality of bodies each of which are magnetically anisotropic, at least partially demagnetizing each of said magnetic bodies to prevent undesirable collisions during subsequent operations therewith, placing said bodies in close proximity to one another, and sintering said bodies into highly coherent bodies.

2. A method of manufacturing sintered permanent magnets comprising the steps, compacting finely-divided permanent magnet forming material selected from the group consisting of MFe O and MFe O in which M is at least one metal selected from the group consisting of barium, strontium, and lead, while in the presence of a magnetic field, into a plurality of bodies each of which are magnetically anisotropic, at least partially demagnetizing each of said magnetic bodies to prevent undesirable collisions during subsequent operations therewith, placing said bodies in close proximity to one another, and sintering said bodies into highly coherent bodies.

3. A method of manufacturing sintered permanent magnets comprising the steps, compacting permanent magnet forming material having a given value of intrinsic coercive force H and selected from the group consisting of MFe O and MFe 0 in which M is at least one metal selected from the group consisting of barium, strontium, and lead, while in the presence of a magnetic field, into a plurality of bodies each of which are magnetically anisotropic, at least partially demagnetizing each of said magnetic bodies in a magnetic field having a strength equal at least to the H value of the material to prevent undesirable collisions during subsequent operations therewith, placing said bodies in close proximity to one another, and sintering said bodies into highly coherent bodies.

References Cited in the file of this patent UNITED STATES PATENTS 1,378,969 Milton May 24, 1921 2,576,679 Guillaud Nov. 27, 1951 2,762,778 Gorter et a1. Sept. 11, 1956 OTHER REFERENCES Philips Technical Review, vol. 13, No. 7, January 1952, pages 194-208.

Phys. Rev., vol. 86, '1952, pages 424 and 425. 

